1. Field of the Invention
The present invention relates to a printing apparatus, and more particularly to a printing apparatus for forming a desired image by coagulating a portion of liquid ink by electrical energizing, and transferring this to a printing object such as paper, to thereby affect printing, and to a printing method therefor.
2. Description of the Related Art
This type of printing apparatus is applicable to many kinds of low volume printing, and is disclosed for example in Published Japanese translation No. Hei 4-504688 of PCT (WO 09011897). This apparatus comprises: a rotation drum with a circumferential surface functioning as a positive electrode; a plurality of negative electrodes arranged at a predetermined spacing in an axial direction of the rotation drum and facing the circumferential surface of the rotation drum by a predetermined distance; an injector for injecting and replenishing liquid ink from a rotation input side to (upstream of) the space between the negative electrodes and the circumferential surface of the rotation drum; a coating unit arranged on the rotation input side (upstream) of the injector for coating an olefinic substance containing a metallic oxide onto the circumferential surface of the rotation drum; an energizer for energizing selected negative electrodes of the plurality of negative electrodes in a condition with ink disposed between the negative electrodes and the positive electrode, to thereby coagulate and adhere part of the ink onto the circumferential surface of the rotation drum to form a desired image; a removal device arranged on a rotation output side (downstream) of the space, for removing residual non-coagulated ink from the circumferential surface of the rotation drum; a transfer device arranged on the rotation output side (downstream) of the removal device for transferring a desired image which has been coagulated and adhered to the circumferential surface of the rotation drum, onto an object to be printed; and a washing device arranged on the rotation output side (downstream) of the transfer device, for washing the circumferential surface of the rotation drum.
With this type of printing apparatus, a portion of the liquid ink filled into the space between the electrodes is coagulated by energizing between the electrodes, and adhered to the circumferential surface of the rotation drum. The ink which has been coagulated by energizing is also adhered to the surroundings of the negative electrode, so that the negative electrode surface is covered. Due to this, energizing is impaired (printing is impaired). This energizing impairment is solved, as disclosed in the beforementioned publication, by washing the negative electrode surface and the surroundings thereof with a rotating brush or the like. At this time, the printing must be interrupted, thus inviting a drop in printing efficiency.
The present invention is aimed at dealing with the abovementioned problems, with the object of suppressing the adherence of coagulated ink to the negative terminal surface and the surroundings thereof. The invention is characterized in that in the abovementioned printing apparatus, on the rotation input side of the plurality of negative electrodes there is provided a discharge port whereby a fluid can be discharged towards the negative electrode surface and the surroundings thereof, and there is provided a fluid supply device for supplying a fluid (which may be a liquid or a gas) to the discharge port.
In the printing apparatus according to the present invention, a fluid is supplied from the fluid supply device to the discharge port, and the fluid flows from the discharge port to the negative electrode surface and the surroundings thereof Therefore, the adhering of ink which has been coagulated by energizing, to the negative electrode surface and the surroundings thereof can be suppressed, or the coagulated ink adhered to the negative electrode surface and the surroundings thereof can be washed off. Hence the operation frequency for removing coagulated ink from the surface of the negative electrode and the surroundings thereof, with a removal device such as a rotating brush can be reduced (or eliminated). Therefore the number of printing interruptions can be reduced (or eliminated) and printing efficiency thus increased.
Furthermore, at the time of executing the present invention, in the case where the fluid supplied to the discharge port is an electrolyte containing practically no coagulating component, and the fluid supply device is configured for continually supplying the fluid, then a solution layer of electrolyte can be continuously formed on the negative electrode side in the space between the electrodes. Moreover a solution layer of ink can be continuously formed on the positive electrode side. Consequently, as well as preventing the adherence of ink to the negative electrode surface and the surroundings thereof by means of the solution layer of electrolyte, energizing between electrodes can be performed through the solution layer of electrolyte and the solution layer of ink. Hence extended continuous printing or repetitive printing becomes possible, enabling an improvement in printing efficiency.
Moreover, at the time of executing the present invention, in the case where the fluid supplied to the discharge port is a washing fluid (for example tap water, or a washing liquid containing a solvent, a surface active agent, or the like), and the fluid supply device is configured for momentarily supply the washing fluid at high pressure, then even if the ink which has been coagulated by energizing between the electrodes, is adhered to the negative electrode surface and the surroundings thereof, this same ink can be removed by momentarily supplying the washing fluid at high pressure at a timing such as a pause in the printing during printing. Hence extended continuous printing or repetitive printing becomes possible, enabling an improvement in printing efficiency.
Furthermore, at the time of executing the present invention, in the case where the fluid supply device incorporates a function for cooling the fluid supplied to the discharge port, the negative electrode surface and the surroundings thereof can also be cooled by the fluid supplied from the discharge port. Hence the coagulation of ink by energizing can be suppressed at the negative electrode surface and the surroundings thereof.